The present invention relates to a lighting control system for controlling the amount of light at a workplane within a room of a building and, more particularly, to such a system which has a compensation apparatus therein for maintaining the light at the workplane constant even though the amount of sunlight entering the building varies.
The ability to control the level of light within a room of a building by use of wall mounted dimmer switch has given rise to the opportunity of automatically controlling the level of light within the room. Such systems attempt to control the output of the artificial lighting sources within the room as the light within the room changes. The amount of light within the room will change as the sunlight entering the room changes.
Known automatic lighting control systems include a sensor for sensing the amount of light within the room and a controller responsive to the light sensor for regulating the power supplied to the artificial lighting sources in an attempt to adjust the light supplied by the artificial light sources as the sunlight entering the room varies.
Unfortunately, the light distribution pattern of the artificial light sources is different from the light distribution pattern with regard to sunlight. Because these patterns are different, the impact that the artificial light source has on the sensor is not the same as the impact that sunlight has on the sensor. Accordingly, the impact which sunlight has on the sensor will cause the sensor to provide a first output characteristic in response to variations in sunlight but the different impact which the artificial light source has on the sensor will cause the sensor to provide a second output characteristic in response to the artificial light source. Consequently, the artificial light source will not be correspondingly adjusted for variations in sunlight so that the amount of light received at a workplane located within the controlled room will not be maintained constant but will rather vary as the amount of sunlight entering the building varies.
The present invention provides a compensation mechanism so that the impact that the artificial lighting source and the sunlight have on the light sensing apparatus will remain substantially constant as sunlight varies and as the artificial light source is adjusted in response to variations in sunlight.